Sri Lankan Prime Minister Ranil Wickremesinghe on Friday said the country needs new laws to deal with threats posed by local terror outfits linked to Islamic State, the group which has claimed responsibility for the Easter bombings that left 253 people dead and several hundreds injured.

"The definition on aiding terrorism is very narrow. Therefore, the laws are not strong to deal with a situation like this," Wickremesinghe said in a televised address.

"We have to widen the scope of these laws to counter global terrorism. Not only they (the terrorists) should be arrested, their assets also need to be confiscated," he added.

The Islamic State group has claimed responsibility for the Easter terror attacks on three Catholic churches and three luxury hotels but the government has blamed a local Islamist extremist group, National Tawheed Jamath (NTJ), for the bombings.

Earlier in an interview to Sky News, the prime minister said the government knew that Sri Lankan nationals who joined the Islamic State had returned, but they could not be arrested as joining a foreign terrorist organisation is not against the law in the island nation.

"We knew they went to Syria... But in our country, to go abroad and return or to take part in a foreign armed uprising is not an offence here," Wickremesinghe said.

"We have no laws which enable us to take into custody people who join foreign terrorist groups. We can take those who are, who belong to terrorist groups operating in Sri Lanka," he told the news channel.

Admitting failure of the Lankan intelligence on the attacks, Wickremesinghe said although he had not been fed with prior information, he as the prime minister takes full responsibility for the failure.

He said although the attacks were carried out in the island nation, they might have been remotely controlled at another country.

The planning of the attack and training might have been in another country, he said, adding, "Without destroying this network we will fail in our task to eliminate global terrorism."

Meanwhile, Finance Minister Mangala Samaraweera said the Easter attacks have caused 30 per cent revenue loss to the country.

"We expect a 30 per cent drop in (tourist) arrivals and that means a loss of about $ 1.5 billion in foreign exchange," he said, adding that the country could take up to two years to fully recover from the Easter attacks.